Color former mixture

ABSTRACT

The invention describes a colour former mixture comprising 
     (a) a compound of formula (1) and/or of formula (2) and/or of formula (3) and 
     (b) a compound of formula (4), 
     or a colour former mixture comprising at least two compounds of component (b). 
     The colour former mixture is suitable for pressure- and particularly for heat-sensitive recording materials and has excellent storage ability and superior paper whiteness.

This is a continuation-in-part of application Ser. No. 08/312,017 filedon Sep. 26, 1994 now abandoned.

The present invention relates to a colour former mixture and the usethereof in pressure-sensitive and particularly in heat-sensitiverecording materials, as well as to novel colour formers and to thepreparation of said novel colour formers.

Colour former mixtures which produce strong and stable dyeings inpressure- and heat-sensitive recording systems are disclosed, interalia, in U.S. Pat. No. 5,071,480.

The object of the present invention is the provision of a colour formermixture, in particular for thermography, which even surpasses the colourformer mixtures of the prior art with respect to storage stability andpaper whiteness (background).

Specifically, the present invention relates to a colour former mixturecomprising

(a) a compound of formula ##STR1## and (b) a compound of formula##STR2## or a colour former system comprising at least two compounds ofcomponents (b), wherein

R₁ is hydrogen, hydroxy, halogen or C₁ -C₄ alkyl;

R₂ is hydrogen; nitro; SO₂ R₄ ; SO₂ OR₅ ; SO₂ NR₆ R₇ ; COR₈ ; CONR₆ R₇ ;or C₁ -C₄ haloalkyl; phenylamino; phenyl-C₁ -C₄ alkylamino; anunsubstituted or halogen- or hydroxy-substituted 2-triazinyl or1-benzotriazolyl radical;

R₃ is halogen; nitro; C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; amino; mono-C₁ -C₄alkylamino; di-C₁ -C₄ alkylamino; or COR₈ ;

R₄ is C₁ -C₈ alkyl; C₁ -C₈ haloalkyl; phenyl or phenyl-C₁ -C₄ alkyl,each unsubstituted or substituted in the phenyl moiety by halogen, C₁-C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy;

R₅ is hydrogen; C₁ -C₈ alkyl; C₁ -C₈ haloalkyl; phenyl or phenyl-C₁ -C₄alkyl, each unsubstituted or substituted in the phenyl moiety byhalogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy;

R₆ and R₇ are each independently of the other hydrogen; or C₁ -C₈ alkyl;or

R₆ and R₇, together with the linking nitrogen atom, are an unsubstitutedor C₁ -C₄ alkyl-substituted pyrrolidino, piperidino, morpholino,thiomorpholino or piperazino ring;

R₈ is hydrogen; hydroxy; C₁ -C₈ alkyl; C₁ -C₈ alkoxy; C₁ -C₈ haloalkyl;unsubstituted phenyl or phenyl which is substituted by halogen, C₁ -C₄alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy; phenyl-C₁ -C₄ alkyl orphenyl-C₁ -C₄ alkoxy;

R₉ and R₁₀ are each independently of the other C₁ -C₈ alkyl; or ##STR3##R₁₁ is hydrogen or C₁ -C₅ alkyl; R₁₂ and R₁₃ are each independently ofthe other hydrogen, alkyl or not more than 12 carbon atoms which isunsubstituted or substituted by halogen, hydroxy, cyano or C₁ -C₅alkoxy; C₅ -C₇ cycloalkyl, or phenylalkyl or phenyl which isunsubstituted or ring-substituted by halogen, cyano, C₁ -C₅ alkyl or C₁-C₅ alkoxy, or

R₁₂ and R₁₃, together with the linking nitrogen atom, are a five- orsix-membered heterocyclic radical;

X₁ and X₂ are each independently of the other hydrogen; C₁ -C₈ alkyl;unsubstituted or C₁ -C₄ alkyl- or halogen-substituted C₄ -C₇ cycloalkyl;unsubstituted phenyl or phenyl which is substituted by C₁ -C₄ alkyl,hydroxy or halogen; phenyl-C₁ -C₄ alkyl; C₃ -C₆ alkenyl; C₁ -C₄ alkoxy;C₁ -C₄ alkoxy-C₁ -C₄ alkyl; 2-tetrahydrofuranyl, or

X₁ and X₂, together with the linking nitrogen atom, are an unsubstitutedor C₁ -C₄ alkyl-substituted pyrrolidino, piperidino, morpholino,thiomorpholino or piperazino ring;

X₃ is hydrogen or C₁ -C₄ alkyl;

X₄ and X₅ are each independently of the other phenyl or phenyl-C₁ -C₄alkyl, each unsubstituted or substituted in the phenyl moiety byhalogen, nitro, C₁ -C₄ alkyl, C₁ -C₄ alkoxy, C₁ -C₄ haloalkyl or --NR₁₂R₁₃ ; a 2-pyrrolyl, 2-thienyl, 2- or 3-indolyl, 2-benzofuranyl or2-naphthothienyl radical;

Y₁ and Y₂ are each independently of the other C₁ -C₅ alkyl;

Y₃ is hydrogen; C₁ -C₅ alkyl, C₅ -C₇ cycloalkyl, unsubstituted phenyl orphenyl which is substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkylor C₁ -C₄ alkoxy;

the benzene ring A may be substituted by halogen; cyano; nitro; C₁ -C₅alkyl; C₁ -C₅ alkoxy; C₁ -C₅ alkylthio; C₁ -C₅ alkylcarbonyl; C₁ -C₅alkoxycarbonyl; or NR₁₂ R₁₃ ; and

n is 0; 1; 2; 3; or 4.

The components of formulae (1), (2), (3) and (4) may be present assingle compounds or as mixtures.

In the literature the individual substituent positions in the fluoranring are numbered differently. In the present specification, thefollowing numbering has been adopted: ##STR4##

Within the scope of the above definition the respective substituentshave the following preferred meanings:

Halogen is fluoro, chloro or bromo, preferably fluoro or chloro.

Within the scope of each definition, alkyl is straight chain or branchedalkyl. Illustrative examples of such alkyl groups are methyl, ethyl,n-propyl, isopropyl, n-butyl, 1-methyl-butyl, sec-butyl, tert-butyl,n-pentyl, amyl, isoamyl, n-hexyl, 2-ethyl-hexyl, n-heptyl, n-octyl,isooctyl, 1,1,3,3-tetramethylbutyl.

Examples of haloalkyl are preferably the C₁ -C₂ haloalkyl radicals, suchas trichloromethyl, trifluoromethyl, dichlorofluoromethyl,difluorochloromethyl, perchloroethyl, 1,1,2,2-tetrachloroethyl,1,1,2,2-tetrafluoroethyl, 2,2,2-trichloroethyl. R₅ as C₁ -C₈ haloalkylis preferably haloalkyl as defined above, but also comprises alkylradicals in which all or at least most of the C--H-bonds are replaced byC--Cl or C--F.

Alkoxy is preferably methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy,isobutoxy, sec-butoxy and tert-butoxy; C₁ -C₄ alkoxy-C₁ -C₄ alkyl ispreferably methoxymethyl, methoxyethyl, ethoxymethyl or ethoxyethyl.

Mono-C₁ -C₅ alkylamino is preferably methylamino, ethylamino,propylamino, butylamino and pentylamino. Di-C₁ -C₅ alkylamino comprisesboth the mixed as well as the corresponding substituted radicals, suchas methylethylamino, dimethylamino, diethylamino, methylpropylamino,methylbutylamino, di-n-propylamino, diisopropylamino, di-n-butylaminoand di-n-pentylamino and the like.

In phenyl-C₁ -C₄ alkyl and phenyl-C₁ -C₄ alkoxy, the phenyl moiety maybe bound through a straight-chain or branched alkyl or alkoxy chain.Phenethyl, benzyl and phenylmethoxy are preferred.

The phenyl moiety in phenyl-C₁ -C₄ alkyl, phenyl-C₁ -C₄ alkoxy andphenyl itself is preferably unsubstituted or carries up to threeidentical or different substituents from among those cited above.

Typical examples of C₃ -C₅ alkenyl are allyl, 1-propenyl or 2-pentenyl,isopropenyl or 2-butenyl. Allyl is preferred. C₄ -C₇ cyclohexyl iscyclobutyl, cyclopentyl, cyclohexyl or cycloheptyl. Cyclohexyl ispreferred.

Of preeminent interest is a colour former mixture comprising

(a) a compound of formula ##STR5## and (b) a compound of formula##STR6## wherein R₁ is hydrogen, hydroxy, halogen or C₁ -C₄ alkyl;

R₂ is hydrogen; nitro; SO₂ R₄ ; SO₂ OR₅ ; SO₂ NR₆ R₇ ; COR₈ ; C₁ -C₄haloalkyl; a 2-triazinyl or 1-benzotriazolyl radical which isunsubstituted or substituted by halogen or hydroxy;

R₃ is halogen; nitro; C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; amino; mono-C₁ -C₄alkylamino; di-C₁ -C₄ alkylamino; or COR₈ ;

R₄ is C₁ -C₈ alkyl; C₁ -C₈ haloalkyl; phenyl or phenyl-C₁ -C₄ alkyl,each unsubstituted or substituted in the phenyl moiety by halogen, C₁-C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy;

R₅ is hydrogen; C₁ -C₈ alkyl; C₁ -C₈ haloalkyl; phenyl or phenyl-C₁ -C₄alkyl, each unsubstituted or substituted in the phenyl moiety byhalogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy;

R₆ and R₇ are each independently of the other hydrogen; or C₁ -C₈ alkyl;or

R₆ and R₇, together with the linking nitrogen atom, are an unsubstitutedor C₁ -C₄ alkyl-substituted pyrrolidino, piperidino, morpholino,thiomorpholino or piperazino ring;

R₈ is hydrogen; hydroxy; C₁ -C₈ alkyl; C₁ -C₈ alkoxy; C₁ -C₈ haloalkyl;unsubstituted phenyl or phenyl which is substituted by halogen, C₁ -C₄alkyl, C₁ -C₄ haloalkyl, C₁ -C₄ alkoxy; phenyl-C₁ -C₄ alkyl or phenyl-C₁-C₄ alkoxy;

R₉ and R₁₀ are each independently of the other C₁ -C₈ alkyl; or ##STR7##R₁₁ is hydrogen or C₁ -C₅ alkyl; R₁₂ and R₁₃ are each independently ofthe other hydrogen, alkyl of at the most 12 carbon atoms which isunsubstituted or substituted by halogen, hydroxy, cyano or C₁ -C₅alkoxy; C₅ -C₇ cycloalkyl, or phenylalkyl or phenyl which isunsubstituted or ring-substituted by halogen, cyano, C₁ -C₅ alkyl or C₁-C₅ alkoxy; or

R₁₂ and R₁₃, together with the linking nitrogen atom, are a five- orsix-membered heterocyclic radical;

X₁ and X₂ are each independently of the other hydrogen; C₁ -C₄ alkyl; C₄-C₇ cycloalkyl which is unsubstituted or substituted by C₁ -C₄ alkyl orhalogen; unsubstituted phenyl or phenyl which is substituted by C₁ -C₄alkyl, hydroxy or halogen; phenyl-C₁ -C₄ alkyl; C₃ -C₆ alkenyl; C₁ -C₄alkoxy; C₁ -C₄ alkoxy-C₁ -C₄ alkyl; 2-tetrahydrofuranyl, or

X₁ and X₂, together with the linking nitrogen atom, are an unsubstitutedor C₁ -C₄ alkyl-substituted pyrrolidino, piperidino, morpholino,thiomorpholino or piperazino ring;

X₃ is hydrogen or C₁ -C₄ alkyl;

X₄ and X₅ are each independently of the other phenyl or phenyl-C₁ -C₄alkyl, each unsubstituted or substituted in the phenyl moiety byhalogen, nitro, C₁ -C₄ alkyl, C₁ -C₄ alkoxy, C₁ -C₄ haloalkyl or --NR₁₂R₁₃ ; a 2-pyrrolyl, 2-thienyl, 2- or 3-indolyl, 2-benzofuranyl or2-naphthothienyl radical;

Y₁ and Y₂ are each independently of the other C₁ -C₅ alkyl;

Y₃ is hydrogen; C₁ -C₅ alkyl; C₅ --C₇ cycloalkyl, unsubstituted phenylor phenyl which is substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄haloalkyl or C₁ -C₄ alkoxy;

the benzene ring A may be substituted by halogen; cyano; nitro; C₁ -C₅alkyl; C₁ -C₅ alkoxy; C₁ -C₅ alkylthio; C₁ -C₅ alkylcarbonyl; C₁ -C₅alkoxycarbonyl; or NR₁₂ R₁₃ ; and

n is 0; 1; 2; 3; or 4.

In component (a) it is preferred to use colour formers of formula (1),wherein

R₁ is hydrogen, halogen or C₁ -C₄ alkyl;

R₂ is nitro; SO₂ R₄ ; SO₂ OR₅ ; SO₂ NR₆ R₇ ; COR₈ ; CONR₆ R₇ ; or C₁ -C₄haloalkyl;

n is 0, 1, 2, 3 or 4;

R₃ if n=1, 2, 3 or 4, is halogen; if n=1 or 2, is C₁ -C₄ alkyl or C₁ -C₄haloalkyl; or if n=1, is nitro, COR₈, amino, mono-C₁ -C₄ alkylamino ordi-C₁ -C₄ alkylamino;

R₄ is C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; phenyl or phenyl-C₁ -C₂ alkyl,each unsubstituted or substituted in the phenyl moiety by halogen, C₁-C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy;

R₅ is hydrogen; C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; phenyl or phenyl-C₁ -C₂alkyl, each unsubstituted or substituted in the phenyl moiety byhalogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy;

R₆ and R₇ are each independently of the other hydrogen; or C₁ -C₄-alkyl; or

R₆ and R₇, together with the linking nitrogen atom, are an unsubstitutedor C₁ -C₄ alkyl-substituted pyrrolidino or piperidino ring;

R₈ is hydrogen; C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; C₁ -C₄ alkoxy;unsubstituted phenyl or phenyl which is substituted by halogen, C₁ -C₄alkyl, C₁ -C₄ haloalkyl, C₁ -C₄ alkoxy; phenyl-C₁ -C₂ alkyl or phenyl-C₁-C₂ alkoxy;

R₉ and R₁₀ are each independently of the other C₁ -C₈ alkyl; or ##STR8##X₁ and X₂ are each independently of the other hydrogen; C₁ -C₅ alkyl; or

X₁ and X₂, together with the linking nitrogen atom, are an unsubstitutedor C₁ -C₄ alkyl-substituted pyrrolidino or piperidino ring; and

X₃ is hydrogen or methyl.

Very particularly preferred are compounds of formula (1), wherein

R₁ is hydrogen or methyl;

R₂ is nitro; SO₂ R₄ ; SO₂ OR₅ ; SO₂ NR₆ R₇ ; COR₈ ; CONR₆ R₇ ; or C₁ -C₄haloalkyl;

n is 0, 1, 2, 3 or 4;

R₃ if n=1, 2, 3 or 4, is halogen; if n=1 or 2, is methyl; or if n=1, isnitro, amino, mono-C₁ -C₄ alkylamino or di-C₁ -C₄ alkylamino;

R₄ is C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; phenyl which is unsubstituted orsubstituted by halogen, C₁ -C₄ alkyl, or C₁ -C₄ alkoxy;

R₅ is hydrogen; C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; phenyl or phenyl-C₁ -C₂alkyl, each unsubstituted or substituted in the phenyl moiety byhalogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy;

R₆ and R₇ are each independently of the other hydrogen; or C₁ -C₄ alkyl;

R₈ is hydrogen; C₁ -C₄ alkyl; C₁ -C₄ alkoxy; unsubstituted phenyl orphenyl which is substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkylor C₁ -C₄ alkoxy; phenyl-C₁ -C₂ alkyl or phenyl-C₁ -C₂ alkoxy;

R₉ and R₁₀ are each independently of the other C₁ -C₅ alkyl; or ##STR9##X₁ and X₂ are each independently of the other hydrogen; C₁ -C₅ alkyl; or

X₁ and X₂, together with the linking nitrogen atom, are an unsubstitutedpyrrolidino or piperidino ring; and

X₃ is hydrogen or methyl.

Important colour formers of formula (1) are those compounds in which

R₂ is COR₈, and

R₈ is hydrogen; C₁ -C₄ alkyl; C₁ -C₄ alkoxy; unsubstituted phenyl orphenyl which is substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkylor C₁ -C₄ alkoxy; phenyl-C₁ -C₂ alkyl or phenyl-C₁ -C₂ alkoxy,

and in particular those compounds of formula (1), wherein

R₈ is C₁ -C₄ alkyl, C₁ -C₄ alkoxy or phenyl-C₁ -C₂ alkoxy.

Preferred colour formers of formula (2) are those compounds in which Riois C₁ -C₈ alkyl.

Colour formers of formula (3) meriting particular interest are thosecompounds wherein

X₄ and X₅ are each independently of the other unsubstituted phenyl orphenyl which is substituted by halogen, nitro, C₁ -C₄ alkyl, C₁ -C₄alkoxy, C₁ -C₄ haloalkyl or --NR₁₂ R₁₃

Y₃ is unsubstituted phenyl or phenyl which is substituted by halogen, C₁-C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy; and

the benzene ring A is substituted by halogen; C₁ -C₅ alkyl; C₁ -C₅alkoxy; or NR₁₃ R₁₄.

Preferred colour formers of component (b) are those compounds of formula(4), wherein

Y₁ and Y₂ are each independently of the other C₃ -C₅ alkyl and

R₉ is C₁ -C₅ alkyl or ##STR10## and R₁₁ is hydrogen or C₁ -C₅ alkyl;

and, in particular, those compounds wherein

Y₁ and Y₂ are each independently of the other C₄ -C₅ alkyl.

Compounds wherein Y₁ and Y₂ have the same meaning are very particularlypreferred.

A particularly preferred colour former mixture comprises as component(a) a compound of formula (1), wherein

R₁ is hydrogen, halogen or methyl;

R₂ is COR₈ ;

n is 0, 1, 2, 3 or 4;

R₃ if n=1, 2, 3 or 4, is halogen; if n=1 or 2, is methyl; or if n=1, isnitro, amino, mono-C₁ -C₄ alkylamino or di-C₁ -C₄ alkylamino;

R₈ is hydrogen; C₁ -C₄ alkyl; C₁ -C₄ alkoxy; unsubstituted phenyl orphenyl substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄alkoxy; phenyl-C₁ -C₂ -alkyl or phenyl-C₁ -C₂ alkoxy;

X₁ and X₂ are each independently of the other hydrogen; C₁ -C₅ alkyl; or

X₁ and X₂, together with the linking nitrogen atom, are an unsubstitutedpyrrolidino or piperidino ring; and

X₃ is hydrogen or methyl;

and/or a compound of formula (2), wherein

R₁₀ is C₁ -C₅ alkyl;

and, as component (b), a compound of formula (4), wherein

Y₁ and Y₂ are C₃ -C₅ alkyl, and

R₉ is C₁ -C₅ alkyl; or ##STR11## and R₁₁ is hydrogen or C₁ -C₅ alkyl.

The compounds of formula (1) are disclosed in EP-A-0 561 738 and can beprepared according to the methods described therein.

The compounds of formula (3) and the preparation thereof are disclosedin U.S. Pat. No. 4,675,497.

Some of the compounds of formula (4) are disclosed in, inter alia, U.S.Pat. No. 5,071,480. Some of the compounds of formula (4) are novel.These novel compounds are also an object of the invention.

These novel compounds correspond to formula ##STR12## wherein X' is C₁-C₅ alkyl; or ##STR13## Y' is C₄ -C₅ alkyl; and R'₁₁ is hydrogen or C₁-C₅ alkyl.

The compounds of formula (4') can be prepared by methods known per se,for example by condensing a benzophenone of formula ##STR14## with aphenol or a phenol ether of formula ##STR15## in the temperature rangefrom preferably 0° to 70° C. in 50 to 100% sulfuric acid, with removalof the formyl protective group, to a phthalide of formula ##STR16## andthen cyclising said compound of formula (III) in the temperature rangefrom 20° to 100° C. to a compound of formula (4'). In the above formulae(I), (II) and (III), X', Y' and R'₁₁ are as defined for formula (4') andR' is hydrogen or C₁ -C₄ alkyl.

This process is also an object of the present invention.

The novel colour former mixture can be prepared by simple mixing andmilling of said components (a) and (b). Homogeneous powder mixtures arethus obtained which are storage stable at room temperature. Theindividual colour former components are preferably milled individuallyin the wet state and then mixed as a dispersion.

The components (a) and (b) are preferably used in crystalline form.

The colour former components (a) and (b) are usually in a weight ratiofrom 1:5 to 1:1 and preferably from 1:3 to 1:2. The desired colourshades can thus be adjusted.

The colour former mixture of this invention is very well suited to thepreparation of pressure-sensitive and in particular of heat-sensitiverecording systems. To this end, the components (a) and (b) can also beused separately.

The colour former mixture of this invention is usually colourless or atmost faintly coloured. When the sublimation-fast colour former mixturesare brought into contact preferably with an acid developer, i.e. anelectron acceptor, they produce deep grey or black images. The colourformer mixtures of this invention are also very useful in admixture withone or more than one other known colour formers, typically3,3-bis(aminophenyl)phthalides such as CVL, 3-indolyl-3-aminophenylaza-or -diazaphthalides, (3,3-bisindolyl)phthalides, 3-aminofluorans,substituted 3,7-diaminofluorans, leukoauramines, spiropyranes,spirodipyranes, chromenopyrazoles, chromenoindoles, phenoxazines,phenothiazines, carbazolyl methanes or other triarylmethaneleuko dyes.

The colour former mixture of this invention exhibits an excellent colourintensity and lightfastness on activated clays as well as on phenolicsubstrates. It is particularly suitable for use as rapidly developingcolour former mixture in a pressure-sensitive or, preferably, in aheat-sensitive recording material which may be a copying material aswell as a recording material. The colour former mixture of thisinvention is storage stable. Compared with the images obtained with asingle component such as 2-phenylamino-3-methyl-6-diethylaminofluoran,the black images obtained with the colour former mixture of thisinvention with phenols exhibit an enhanced storage stability as well asslighter background discoloration.

A pressure-sensitive material typically comprises at least one pair ofsheets that contain one colour former mixture of components (a) and (b)dissolved in an organic solvent, and an electron acceptor as developer.

Typical examples of such developers are active clays such as attapulgiteclay, acid clay, bentonite, montmorillonite, activated clay such asacid-activated bentonite or montmorillonite, and also zeolite,halloysite, silica, alumina, aluminium sulfate, aluminium phosphate,zinc chloride, zinc nitrate, zirconium dioxide, activated kaolin or anyclay. As developers it is also possible to use acidic organic compoundssuch as ring-substituted phenols, resorcinols, salicylic acids,including 3,5-bis(α,α-dimethylbenzyl)salicylic acid or3,5-bis(α-methylbenzyl)salicylic acid or salicylates and their metalsalts, e.g. zinc salts, as well as an acidic polymeric material such asa phenolic polymer, an alkyl phenol acetylene resin, a maleic acid rosinresin or a partially or completely hydrolysed polymer of maleicanhydride with styrene, ethylene or vinyl methyl ether, orcarboxymethylene. Mixtures of the cited monomers and polymers can alsobe used. Particularly preferred developers are acid-activated bentonite,zinc salicylates or the condensates of p-substituted phenols withformaldehyde. These last mentioned compounds may also be modified withzinc. Zinc salicylates are disclosed, inter alia, in EP-A-181 283 orDE-A-2 242 250.

The developers may also be used in admixture with other basically inertor substantially inert pigments or with other auxiliaries such as silicagel or UV absorbers, e.g. 2-(2'-hydroxyphenyl)benzotriazoles. Examplesof such pigments are: talcum, titanium dioxide, alumina, aluminiumhydroxide, zinc oxide, chalk, clays such as kaolin, as well as organicpigments, e.g. urea/formaldehyde condensates (BET surface area: 2-75 m²/g) or melamine/formaldehyde condensates.

The colour former mixture produces a coloured image at those pointswhere it comes into contact with the electron acceptor. To prevent thecolour formers contained in the pressure-sensitive recording materialfrom becoming active prematurely, they are usually separated from theelectron acceptor. This separation can conveniently be accomplished byincorporating the colour formers in foam-like, sponge-like orhoneycomb-like structures. The colour formers are preferablyencapsulated in microcapsules, which can normally be ruptured bypressure.

When the capsules are ruptured by pressure, for example with a pencil,the colour former solution is transferred to an adjacent sheet which iscoated with an electron acceptor and a coloured image is thus produced.The colour results from the dye which is formed and which is absorbed inthe visible range of the electromagnetic spectrum.

The colour former mixture is encapsulated preferably in the form ofsolutions in organic solvents. Examples of suitable solvents arepreferably non-volatile solvents, for example a halogenated paraffin,benzene or diphenyl, for example chloroparaffin, trichlorobenzene,monochlorodiphenyl, dichlorodiphenyl or trichlorodiphenyl, and alsoesters such as tricresyl phosphate, di-n-butyl phthalate, dioctylphthalate, trichloroethylphosphate, an aromatic ether such asbenzylphenyl ether, a hydrocarbon oil such as paraffin or kerosene,aromatic hydrocarbons, an alkylated derivative (e.g. comprisingisopropyl, isobutyl, sec- or tert-butyl groups) of diphenyl, naphthaleneor terphenyl; dibenzyl toluene, partially hydrogenated terphenyl, mono-to tetra-C₁ -C₃ alkylated diphenylalkanes, dodecylbenzene, benzylatedxylenes, phenyl xylyl ethane or other chlorinated or hydrogenatedcondensed aromatic hydrocarbons. Mixtures of different solvents,especially mixtures of paraffin oils or kerosene anddiisopropylnaphthalene or partially hydrogenated terphenyl, are oftenused to obtain optimum solubility of the colour formers, a rapid andintense coloration, and a viscosity which is advantageous for themicroencapsulation.

The capsule wails can be formed evenly around the droplets of the colourformer solution by coacervation. The encapsulating material is describede.g. in U.S. Pat. No. 2,800,457. The capsules may also be convenientlyformed from an aminoplast or a modified aminoplast by polycondensation,as described in British patent specifications 989 264, 1 156 725, 1 301052 and 1 355 124. Microcapsules which are formed by interfacialpolymerisation are also suitable, e.g. capsules formed from polyester,polycarbonate, polysulfonamide, polysulfonate, but preferably frompolyamide or polyurethane.

The microcapsules containing the colour former mixture can be used forthe production of a wide variety of known kinds of pressure-sensitivecopying material. The various systems differ substantially from oneanother in the arrangement of the capsules, of the colour reactants, andof the support. A preferred arrangement is that in which theencapsulated colour former mixture is in the form of a layer on the backof a transfer sheet and the electron acceptor is in the form of a layeron the face of a receiver sheet.

Another arrangement of the components is that wherein the microcapsuleswhich contain the colour former mixture, and the developer, are in or onthe same sheet in the form of one or more individual layers, or thedeveloper is incorporated in the support.

The capsules are preferably secured to the support by means of asuitable binder. As paper is the preferred support, these binders areprincipally paper-coating agents such as gum arabic, polyvinyl alcohol,hydroxymethyl cellulose, casein, methyl cellulose, dextrin, starch orstarch derivatives or polymer latices. These latter are typicallybutadiene/styrene copolymers or acrylic homopolymers or copolymers.

The paper employed comprises not only normal paper made from cellulosefibres, but also paper in which the cellulose fibres are replaced(partially or completely) by synthetic polymer fibres. The support mayalso be a plastic sheet.

The colour former mixture of this invention may particularly be used ina thermoreactive recording material. Components (a) and (b) of the novelmixture then develop colour at the same temperature, preferably at 110°to 200° C. The thermoreactive recording material usually comprises atleast one layer support, the colour former mixture, an electron acceptorand optionally also a binder and/or wax. If desired, activators orsensitisers may also be present in the recording material.

Thermoreactive recording systems comprise, for example, heat-sensitiverecording or copying materials and papers. These systems are used e.g.for recording information, for example in electronic computers,teleprinters or telewriters, or in recording and measuring instruments,e.g. electrocardiographs. The image formation (marking) can also beeffected manually with a heated pen. Laser beams can also be used toproduce heat-induced images.

The composition of the thermoreactive recording material may be suchthat the colour former is dispersed or dissolved in one binder layer andthe developer is dissolved or dispersed in the binder in a second layer.Another possibility comprises dispersing both the colour former and thedeveloper in one layer. By means of heat the layer or layers aresoftened at specific areas and the desired colour develops at once atthose areas where heat is applied.

Suitable developers are the same electron acceptors as are used inpressure-sensitive papers. Examples of developers are the clays andphenolic resins already mentioned, or also the phenolic compoundsdisclosed e.g. in German Offenlegungsschrift 1 251 348, for example4-tert-butylphenol, 4-phenylphenol, methylene bis(p-phenylphenol),4-hydroxydiphenyl ether, α-naphthol, β-naphthol, methyl or benzyl4-hydroxybenzoate, 4-hydroxydiphenylsulfone,4-hydroxy-4'-methyldiphenylsulfone,4'-hydroxy-4-isopropoxydiphenylsulfone, 4,4'-cyclohexylidenediphenol,4,4'-isopropylidenediphenol, 4,4'-isopropylidene-bis(2-methylphenol), anantipyrine complex of zinc thiocyanate, a pyridine complex of zincthiocyanate, 4,4'-bis(hydroxyphenyl)valeric acid, hydroquinone,pyrogallol, phloroglucinol, p-, m- and o-hydroxybenzoic acid,hydroxyphthalic acid, gallic acid, 1-hydroxy-2-naphthoic acid, as wellas boric acid or organic, preferably aliphatic, dicarboxylic acids, forexample tartaric acid, oxalic acid, maleic acid, citric acid, citraconicacid or succinic acid.

Fusible, film-forming binders may also be used for making thethermoreactive recording material. These binders are usuallywater-soluble, whereas the colour formers and the developer aresparingly soluble or insoluble in water. The binder should be able todisperse and fix the colour former and the developer at roomtemperature.

When heated, the mixture comprising the coreactand, aktivator and colourformer yysoftens or melts, so that the colour former mixture comes incontact with the developer and a colour is able to form.

Aktivators used in the present colour former mixture are dimethylterephthalate, benzylbenzyloxybenzoate, dibenzyl terephthalate,phenyl-1-hydroxy-2-naphthoate, p-benzylbiphenyl,2,6-di-tert-butyl-p-cresol, phenyl salicylate, benzophenone,N-phenylbenzenesulfonamide, phenyl-1-hydroxy-2-naphthoate or4'4-dibutoxydiphenylsulfone. The activators are preferably auseful forreduction of the melting point of the colour former mixture.

If the colour former mixture and the developer are in two separatelayers, it is possible to use water-insoluble binders, i.e. binderswhich are soluble in non-polar or only weakly polar solvents, forexample natural rubber, synthetic rubber, chlorinated rubber, alkydresins, polystyrene, styrene/butadiene copolymers, polymethylacrylates,ethyl cellulose, nitrocellulose and polyvinyl carbazole. The preferredarrangement, however, is that in which the colour former mixture and thedeveloper are contained in one layer in a water-soluble binder.

To ensure the stability of the heat-sensitive recording material or thedensity of the developed image, the material may be provided with anadditional protective layer. Such a protective layer will normallyconsist of water-soluble and/or water-insoluble resins which areconventional polymeric materials or aqueous emulsions of these polymericmaterials.

The thermoreactive layers and resin coatings may comprise furtherauxiliaries. To improve the degree of whiteness, to facilitate theprinting of papers, and to prevent the heated pen from sticking, theselayers may comprise e.g. talcum, titanium dioxide, zinc oxide, aluminiumhydroxide, calcium carbonate (e.g. chalk), clays or also organicpigments, for example urea/formaldehyde polymers. To effect the colourformation only within a limited temperature range it is possible to addsubstances such as urea, thiourea, diphenyl thiourea, acetamide,acetanilide, benzene sulfanilide, stearamide,bis(stearoyl)ethylenediamide, phthalic anhydride, metal stearates suchas zinc stearate, phthalonitrile, dimethyl terephthalate, dibenzylterephthalate or other appropriate fusible products which induce thesimultaneous melting of the colour former and the developer.Thermographic recording materials preferably comprise waxes, e.g.carnauba wax, montan wax, paraffin wax, polyethylene wax, condensates ofhigher fatty acid amides and formaldehyde, or condensates of higherfatty acids and ethylenediamine.

Pressure-sensitive and particularly heat-sensitive recording materialsof this invention have excellent storage ability and superior paperwhiteness (background).

In the following working and application Examples percentages are byweight, unless otherwise indicated.

PREPARATION OF THE NOVEL COMPOUNDS Example 1

55.4 g of 4'-dibutylamino-2-hydroxybenzophenone-2-carboxylic acid aredissolved at 40° C. in 217 g of 98% sulfuric acid. To this solution areadded 21 g of N-methyl-p-anisidine at c. 10° C. and the mixture isstirred for 20 hours at 20°-25° C. The resultant reaction solution ischarged to a readily stirrable mixture of 700 ml of water, 800 ml oftoluene and 455 ml of 10N aqueous sodium hydroxide. The batch is keptfor one hour at reflux at c. 83° C. and the aqueous phase is thenseparated at c. 70° C. The toluene phase is washed with 2×150 ml ofwater and the toluene is then distilled off under reduced pressure,giving 65.4 g of the crude product of formula ##STR17## which, afterrecrystallisation from a mixture of isopropyl alcohol und toluene, has amelting point of 217°-218° C.

On commercial CF papers as well as in thermoapplication this compounddevelops an olive-green image on a white background (optical density:0.008 Db (Db="density black"); measurement is carried out with a GRETAG®SPM100 densitometer; q.v. Example 10).

Example 2

22.2 g of 3'-dibutylamino-2-hydroxybenzophenone-2-carboxylic acid aredissolved at c. 40° C. in 87 g of 98% sulfuric acid. Over 30 minutes,9.9 g of N-formyl-N-methyl-p-anisidine are added to this solution at c.10° C. The reaction mass is stirred for 20 hours at 20°-25° C. Theformyl protective group is removed by cautiously adding 40 ml of waterdropwise and keeping the temperature at c. 100° C. for 1 hour. Theresultant solution is then poured into a mixture of 100 ml of water, 400ml of toluene and 182 ml of 10N aqueous sodium hydroxide (pH=c. 10-11)and kept for 1 hour at reflux. The aqueous phase is separated at 75° C.The toluene phase is washed with 2×200 ml of water at 75° C. and, afterremoval of the water as an azeotrope, clarified by filtration. Thetoluene is distilled off and the residue is crystallised in methane,giving 21.9 g of the product of formula (101), which has propertiesidentical to those of this compound.

Examples 3 to 9

The following compounds are prepared (Table 1) in general accordancewith the procedure of Example 1:

                  TABLE 1                                                         ______________________________________                                         ##STR18##                                                                            compound                     mp                                       Example of formula                                                                              R        R.sub.2    °C.!                             ______________________________________                                        3       (102)     n-butyl  ethyl     160-162                                  4       (103)     n-butyl  n-butyl   138-139                                  5       (104)     n-butyl  sec-butyl 113-114                                  6       (105)     n-butyl  isopropyl 148-149                                  7       (106)     ethyl    isopropyl 166-169                                  8       (107)     n-pentyl methyl    162-164                                  9       (108)     ethyl    CH.sub.2 C(CH.sub.3).sub.3                                                              137-140                                  ______________________________________                                    

Example 10a

73.9 g of 3'-dibutylamino-2-hydroxybenzophenone-2-carboxylic acid aredissolved at a maximum temperature of 40° C. in 295 g of 100% sulfuricacid. The solution is cooled to c. 10° C. and 33 g ofN-formyl-N-methyl-p-anisidine are added over c. 30 minutes. The reactionmass is stirred for 20 minutes at 20°-25° C. and then poured into 1000ml of water and 800 g of ice at 0°-10° C.

The suspension is stirred for 1.5 hours, then filtered at 10° C. and thefilter product is washed with 400 ml of cold water.

The moist filter cake of formula ##STR19## is added to a mixture of 400ml of toluene, and

100 ml of water, and

53 g of sodium carbonate, heated to reflux (c. 81° C.) and kept at thistemperature for 7 hours. The toluene phase is separated and washed withwater, then dried azeotropically, clarified by filtration with activatedcarbon and concentrated. The resultant residue weighs 50 g and isrecrystallised from isopropyl alcohol, giving colourless crystals of thefluoran of formula ##STR20## with a melting point of 193° to 194° C.

Example 10b

The phthalide compound of formula (109a) may also be cyclised to thefluoran of formula (109) by boiling for 2 hours in dimethyl formamide(DMP) at 147°-149° C.

Yield: 95% of theory.

Example 11

20 g of the fluoran of formula (101) are added to 50 ml of technicalgrade 85% formic acid and heated to reflux temperature (c. 97° C.).After 20 minutes the formylation reaction is complete and the resultantred solution is poured into 1 liter of ice-water at c. 10° C. The batchis allowed to warm to 20°-25° C. and then filtered. The filter productis washed on a suction filter and dried under vacuum at 70° C., giving18.5 g of a pale pink product of formula (109) with a melting point of192° to 194° C.

This compound develops a deep red image on commercial CF papers.

In thermoapplication a red image is obtained on a white background(Dm=0.07; Dm="density magenta") likewise. Storage testing of thisthermal paper gives excellent results: Dm=0.08 is measured after 1 hourat 58° C. and 50% relative humidity. Dm=1.23 is obtained, with afacsilime machine.

APPLICATION EXAMPLES Example 12

Use in Thermography

a) Preparation of dispersion (A):

1.3 g of the olive colour former of formula (101), and 0.7 g of theorange colour former of formula ##STR21## are milled at room temperaturein a ball mill with 7 g of an aqueous 10% solution of polyvinyl alcoholand 4 g of water to a particle size of 1-4 μm.

b) Preparation of dispersion (B):

2 g of 4,4'-isopropylidene diphenol (bisphenol A) are milled at roomtemperature with 7 g of an aqueous 10% solution of polyvinyl alcoholV03/140 and 4 g of water to a particle size of 2 to 4 μm.

3 parts by weight of dispersion (B) and 1 part by weight of dispersion(A) are mixed thoroughly and then coated on a paper with a coating knifeto give a dry coating weight of c. 0.6 g/m² after drying in the air. Thepaper is kept for 24 hours at 23° C. and 56% relative humidity.

Background colour: 0.06 Db (measurement of the Db value is carded outwith a densitometer GRETAG® SPM 100 densitometer).

Black writing with an optical densitiy of Db 1.10 is produced with acommercially available facsimile machine (INFOTEC® 6510).

The dried paper is stored for 1 hour at 58° C. and 50% relative humidityto give a Db value of 0.10.

Example 13

The procedure of Example 12 is repeated except that the colour formercomponents (a) and (b) are milled at first individually and subsequentlymixed. The results obtained in Example 12 can thus even be surpassed.

Example 14

1.5 g of the colour former of formula (101) are milled at roomtemperature in a ball mill with 5.25 g of an aqueous 10% solution ofpolyvinyl alcohol and 3 g of water to a particle size of 1-4 μm.

0.5 g of tahe compound of formula (111) was milled at room temperaturein a second ball mill with 1.75 g of an aqueous 10% solution ofpolyvinyl alcohol and 1 g of water to a particle size of 1-4 μm.

The colour formers so obtained are then mixed (=dispersion 14A).

3 parts by weight of dispersion B of Example 12 are added to 1 part byweight of dispersion (14A) and the mixture is stirred thoroughly. Asdescribed in Example 12, this mixture is coated on a paper and dried.When using a facsimile machine, black writing with an optical density of1.15 Db develops. The background is white and has an optical density of0.07 Db.

Example 15

The procedure of Example 12, is repeated but using 0.7 g of3-cyclohexyl-amino-6-chlorofluoran instead of the orange colour formerof formula (110) for the preparation of dispersion (A). When using afacsimile machine, black writing on a white background is obtained.

Example 16

Example 12 is repeated, but using a mixture of colour formers of

1.8 parts by weight of the colour former of formula (101),

0.9 part by weight of the colour former of formula (110), and

0.3 part by weight of the colour former of formula ##STR22## for thepreparation of dispersion (A). When using a facsimile machine, blackwriting on a white background is obtained.

Example 17

The procedure of Example 12 is repeated, but using a mixture of colourformers of

1.8 parts by weight of the colour former of formula (101),

0.9 part by weight of the colour former of formula (110), and

0.3 part by weight of the colour former of formula ##STR23## for thepreparation of dispersion (A). When using a facsimile machine, blackwriting on a white background is obtained.

Example 18

The procedure of Example 12 is repeated, but using a mixture of colourformers of

1.8 parts by weight of the colour formers of formula (101),

0.9 part by weight of the colour former of formula (110), and

0.3 part by weight of the colour former of formula ##STR24## for thepreparation of dispersion (A). When using a facsimile machine, blackwriting on a white background is obtained.

Example 19

Instead of dispersion (B) of Example 12, the following basic formulationconsisting of the following components may be used:

    ______________________________________                                                            Conc.                                                                              Solids                                                                    %!   g!                                                  ______________________________________                                        co-reactant bisphenol A or                                                                          33.3   7.5                                              2,2,-bis-4-hydroxy-4-methylpentane*                                           benzylbiphenyl activator                                                                            25     8                                                MgCO.sub.3 *          25     6.8                                              potato starch         12     16.7                                             zinc stearate*        20     2.5                                              titanium dioxide*     25     1.6                                              whitener of the sulfonated stilbene                                                                 25     0.6                                              type                                                                          carboxylated styrene-butadiene                                                                      50     2                                                copolymer                                                                     deionised water       100    33.14                                            ______________________________________                                    

This basic formulation is prepared as follows: The starred singlecomponents are dispersed with a commercial surfactant. Deionised wateris then added to this dispersion and the remaining components aresubsequently added.

Example 20

Instead of the activators, pigments and co-reactants of Example 20,basic formulations containing the following single compounds are used:

pigments: CaCO₃ ; urea/formaldehyde condensate

coreactant: 2,4-dihydroxybenzophenone;

activators: dimethyl terephthalate; benzylbenzyloxybenzoate; dibenzylterephthalate; phenyl-1-oxy-2-naphthoate; p-benzylbiphenyl;2,6-di-tert-butyl-p-cresol; phenyl salicylate; benzophenone;N-phenylbenzenesulfonamides; phenyl-1-hydroxy-2-naphthoates;4'4-dibutoxydiphenylsulfone.

Example 21

Application to copying systems

A solution of 2.2 g of the compound of formula (103), 1.4 g of thecompound of formula (110), 0.6 g of3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide and 0.8 g ofN-butylcarbazole-3-yl-bis(4-N-methyl-N-phenylaminophenyl)methane in 80 gof diisopropylnaphthalene and 19 g of kerosene is encapsulated bycoacervation by per se known method with gelatine and gum arabic, mixedwith a solution of starch and then coated on a sheet of paper. The faceof a second sheet of paper is coated with activated clay as colourdeveloper. The first sheet containing the sublimation-fast colour formerand the sheet coated with the colour developer are laid on top of eachother with their coated sides face to face. Pressure is then exertedonto the first sheet by handwriting or by typewriter and a deep blackcopy of excellent lightfastness develops immediately on the sheet coatedwith the developer.

What is claimed is:
 1. A colour former mixture, comprising(a) a compoundof formula ##STR25## and (b) a compound of formula ##STR26## wherein R₁is hydrogen, hydroxy, halogen or C₁ -C₄ alkyl; R₂ is hydrogen; nitro;SO₂ R₄ ; SO₂ OR₅ ; SO₂ NR₆ R₇ ; COR₈ ; CONR₆ R₇ ; or C₁ -C₄ haloalkyl;phenylamino; phenyl-C₁ -C₄ -alkylamino; an unsubstituted or halogen- orhydroxy-substituted 2-triazinyl or 1-benzotriazolyl radical; R₃ ishalogen; nitro; C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; amino; mono-C₁ -C₄alkylamino; di-C₁ -C₄ alkylamino; or COR₈ ; R₄ is C₁ -C₈ alkyl; C₁ -C₈haloalkyl; phenyl or phenyl-C₁ -C₄ alkyl, each unsubstituted orsubstituted in the phenyl moiety by halogen, C₁ -C₄ alkyl, C₁ -C₄haloalkyl or C₁ -C₄ alkoxy; R₅ is hydrogen; C₁ -C₈ alkyl; C₁ -C₈haloalkyl; phenyl or phenyl-C₁ -C₄ alkyl, each unsubstituted orsubstituted in the phenyl moiety by halogen, C₁ -C₄ alkyl, C₁ -C₄haloalkyl or C₁ -C₄ alkoxy; R₆ and R₇ are each independently of theother hydrogen or C₁ -C₈ alkyl; or R₆ and R₇, together with the linkingnitrogen atom, are an unsubstituted or C₁ -C₄ alkyl-substitutedpyrrolidino, piperidino, morpholino, thiomorpholino or piperazino ring;R₈ is hydrogen; hydroxy; C₁ -C₈ alkyl; C₁ -C₈ alkoxy; C₁ -C₈ haloalkyl;phenyl which is unsubstituted or substituted by halogen, C₁ -C₄ alkyl,C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy; phenyl-C₁ -C₄ alkyl or phenyl-C₁ -C₄alkoxy; X₁ and X₂ are each independently of the other hydrogen; C₁ -C₈akyl; C₄ -C₇ cycloalkyl which is unsubstituted or substituted by C₁ -C₄alkyl or halogen; unsubstituted phenyl or phenyl which is substituted byC₁ -C₄ alkyl, hydroxy or halogen; phenyl-C₁ -C₄ alkyl; C₃ -C₆ alkenyl;C₁ -C₄ alkoxy; C₁ -C₄ alkoxy-C₁ -C₄ alkyl; 2-tetrahydrofuranyl, or X₁and X₂, together with the linking nitrogen atom, are an unsubstituted orC₁ -C₄ alkyl-substituted pyrrolidino, piperidino, morpholino,thiomorpholino or piperazino ring; X' is C₁ -C₅ alkyl; or --(CO)H; Y' isC₄ -C₅ alkyl; R₁₁ is hydrogen or C₁ -C₅ alkyl; and n is 0; 1; 2; 3; or4.
 2. A colour former mixture according to claim 1, wherein in formula(1)R₁ is hydrogen, halogen or C₁ -C₄ alkyl; R₂ is nitro; SO₂ R₄ ; SO₂OR₅ ; SO₂ NR₆ R₇ ; COR₈ ; CONR₆ R₇ ; or C₁ -C₄ haloalkyl; n is 0, 1, 2,3 or 4; R₃ if n=1, 2, 3 or 4, is halogen; if n=1 or 2, is C₁ -C₄ alkylor C₁ -C₄ haloalkyl; or if n=1, is nitro, COR₈, amino, mono-C₁ -C₄alkylamino or di-C₁ -C₄ alkylamino; R₄ i C₁ -C₄ alkyl; C₁ -C₄ haloalkyl;phenyl or phenyl-C₁ -C₂ alkyl, each unsubstituted or substituted in thephenyl moiety by halogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄alkoxy; R₅ is hydrogen; C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; phenyl orphenyl-C₁ -C₂ alkyl, each unsubstituted or substituted in the phenylmoiety by halogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy; R₆and R₇ are each independently of the other hydrogen; or C₁ -C₄ -alkyl;or R₆ and R₇, together with the linking nitrogen atom, are anunsubstituted or C₁ -C₄ alkyl-substituted pyrrolidino or piperidinoring; R₈ is hydrogen; C₁ -C₄ alkyl; C₁ -C₄ haloalkyl; C₁ -C₄ alkoxy;unsubstituted phenyl or phenyl which is substituted by halogen, C₁ -C₄alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy; phenyl-C₁ -C₂ alkyl orphenyl-C₁ -C₂ alkoxy; R₉ and R₁₀ are each independently of the other C₁-C₈ alkyl; or ##STR27## X₁ and X₂ are each independently of the otherhydrogen; C₁ -C₅ -alkyl; or X₁ and X₂, together with the linkingnitrogen atom, are an unsubstituted or C₁ -C₄ alkyl-substitutedpyrrolidino or piperidino ring; and X₃ is hydrogen or methyl.
 3. Acolour former mixture according to claim 1, wherein in formula (1)R₁ ishydrogen or methyl; R₂ is nitro; SO₂ R_(4;) SO₂ OR₅ ; SO₂ NR₆ R₇ ; COR₈; CONR₆ R₇ ; or C₁ -C₄ haloalkyl; n is 0, 1, 2, 3 or 4; R₃ if n=1, 2, 3or 4, is halogen; if n=1 or 2, is methyl; or if n=1, is nitro, amino,mono-C₁ -C₄ -alkylamino or di-C₁ -C₄ alkylamino; R₄ is C₁ -C₄ alkyl; C₁-C₄ haloalkyl; unsubstituted phenyl or phenyl which is substituted byhalogen, C₁ -C₄ alkyl or C₁ -C₄ alkoxy; R₅ is hydrogen; C₁ -C₄ alkyl; C₁-C₄ haloalkyl; phenyl or phenyl-C₁ -C₂ alkyl, each unsubstituted orsubstituted in the phenyl moiety by halogen, C₁ -C₄ alkyl, C₁ -C₄haloalkyl or C₁ -C₄ alkoxy; R₆ and R₇ are each independently of theother hydrogen; or C₁ -C₄ alkyl; R₈ is hydrogen; C₁ -C₄ alkyl;unsubstituted phenyl or phenyl which is substituted by halogen, C₁ -C₄alkyl, C₁ -C₄ haloalkyl or C₁ -C₄ alkoxy; phenyl-C₁ -C₂ alkyl orphenyl-C₁ -C₂ alkoxy; R₉ and R₁₀ are each independently of the other C₁-C₈ alkyl; or ##STR28## X₁ and X₂ are each independently of the otherhydrogen; C₁ -C₅ alkyl; or X₁ and X₂, together with the linking nitrogenatom, are an unsubstituted pyrrolidino or piperidino ring; and X₃ ishydrogen or methyl.
 4. A colour former mixture according to claim 1,comprising a colour former of formula (1), whereinR₂ is COR₈, R₈ ishydrogen; C₁ -C₄ alkyl; C₁ -C₄ alkoxy; unsubstituted phenyl or phenylwhich is substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkyl or C₁-C₄ alkoxy; phenyl-C₁ -C₂ alkyl or phenyl-C₁ -C₂ alkoxy, R₂ is COR₈ andR₈ is hydrogen; C₁ -C₄ alkyl; C₁ -C₄ alkoxy; phenyl which isunsubstituted or substituted by halogen, C₁ -C₄ alkyl, C₁ -C₄ haloalkylor C₁ -C₄ alkoxy; phenyl-C₁ -C₂ alkyl or phenyl-C₁ -C₂ alkoxy.
 5. Acolour former mixture according to claim 1, wherein the weight ratio of(a):(b) is 1:5 to 1:1.
 6. A colour former mixture according to claim 1,wherein components (a) and (b) are in crystalline form.
 7. Apressure-sensitive recording material comprising a support materialcontaining a colour former mixture according to claim
 1. 8. Aheat-sensitive colour former material comprising a support materialcontaining a colour former mixture according to claim
 1. 9. Aheat-sensitive recording material according to claim 8, consisting of aheat-sensitive layer comprising the colour former mixture and adeveloper for the colour former mixture.
 10. A colour former mixtureaccording to claim 1, wherein, in formula (1), R₂ is hydrogen; nitro;SO₂ R₄ ; SO₂ OR₅ ; SO₂ NR₆ R₇ ; COR₈ ; CONR₆ R₇ ; C₁ -C₄ haloalkyl; oran unsubstituted or halogen- or hydroxy-substituted 2-triazinyl or1-benzotriazolyl radical.
 11. A microencapsulated solution comprising acolour former mixture according to claim 1.